Method for making smart cards capable of operating with and without contact

ABSTRACT

The invention concerns a method for making smart cards capable of operating with or without contact called mixed cards and contactless smart cards. In order to avoid the risk of deteriorating the antenna the method consists in producing an antenna comprising at least two turns, on a support sheet, said antenna having its turns located outside the connecting pads, and in providing an insulating bridge so as to connect each of the antenna ends to a connection pad respectively.

This application is a divisional of application Ser. No. 09/545,288filed Apr. 7, 2000, which is based on French Patent Application No.97/12530, filed Oct. 8, 1997.

BACKGROUND

1. Field of the Invention

The invention concerns the manufacture of smart cards capable ofoperating with or without contact. These cards are provided with anantenna integrated in the card and a micromodule connected to theantenna. Information is exchanged with the exterior either by theantenna (therefore without contact) or by contacts flush with thesurface of the card.

Throughout the rest of the description this type of card will be calleda mixed card or mixed smart card.

The manufacturing method also concerns contactless smart cards, that issmart cards capable of operating without contact, information beingexchanged with the exterior only through the antenna.

However, to simplify the following explanation only mixed cards will bereferred to in what follows, although the method also extends tocontactless smart cards, as has just been stated.

2. Related Background

Mixed smart cards are intended to facilitate various operations, such asbanking operations, telephonic communications, identificationoperations, operations for discharging or recharging units for account,and all kinds of operations which can be carried out either by insertingthe card in a reader or remotely by electromagnetic coupling (inprinciple of the inductive type) between an emitter-receiver terminaland a card placed within the field of action of this terminal.

Mixed cards must have standardised dimensions identical to those ofconventional smart cards fitted with contacts. This is also desirablefor cards operating only without contact.

It will be recalled that cards with contact are defined by the usualstandard ISO 7810, this definition being: a card which is 85 mm long, 54mm wide and 0.76 mm thick. The flush contacts are at clearly definedpositions on the surface of the card.

These standards impose severe constraints on manufacture. In particular,the very low thickness of the card (800 μm) is a major constraint, stillmore severe for mixed cards than for cards simply fitted with contacts,as incorporation of an antenna in the card must be provided for.

The technical problems which are posed are problems of positioning theantenna in relation to the card, as the antenna occupies almost thewhole surface of the card, problems of positioning the integratedcircuit module (comprising the microchip and its contacts) which makespossible the electronic operation of the card, and problems of theprecision and reliability of the connection between the module and theantenna; finally, constraints of mechanical strength, reliability andmanufacturing cost have to be taken into account.

The antenna is generally formed by a conductive element deposited as athin layer on a plastic support sheet. At the ends of the antennaconnecting pads are provided; these must be exposed in order to be ableto connect with the contacts of the electronic module.

In the following description the conductive element forming the antennawill be called the antenna filament, given that, depending on thetechnology used, it may comprise a filament inlaid in the support sheetor printed tracks.

One approved solution for manufacturing mixed smart cards consists inusing plastic foils pre-perforated in the area of the connecting pads ofthe antenna formed by the two ends of the antenna filament, insuperimposing them on the sheet supporting the antenna and in assemblingthem by hot or cold lamination. The position of the connection pads ofthe antenna is limited by the position of the electronic module which isitself defined by the ISO standards.

A cavity to accommodate the electronic module must then be machined inthe body of the card, between the connection pads of the antenna andabove the perforations formed in the plastic foils covering the antenna;then the contacts of the electronic module must be connected to theconnection pads of the antenna by depositing a conductive adhesive inthe perforations. The antenna filament generally comprises severalturns. These turns pass between the connection pads in such a way thatthey can be connected to these pads, which are located near themicromodule.

A first problem then arises from the nature of this structure. The turnsmay be damaged when the cavity is machined. Indeed, the turns can evenbe destroyed during this stage if the antenna is not positioned veryprecisely in relation to the position of the cavity.

SUMMARY

The invention provides a solution for this first problem of the risk ofdamaging or even destroying the antenna. To this end the inventionproposes a manufacturing method for smart cards, the said smart cardcomprising an antenna at the ends of which pads are provided forconnection to an electronic module, characterised in that the methodincludes at least one stage consisting in producing the antennacomprising at least two turns, on a support sheet, the said antennahaving its turns located outside the connecting pads, and in providingan insulating bridge so as to connect each of the antenna ends to aconnection pad respectively.

This stage of the manufacturing method enables a free space to beprovided between the connection pads of the antenna, in which space itis possible to form a cavity for the module without risk of damaging theturns of the antenna.

The insulating bridge is produced by covering the turns of the antennawith an insulating layer in one zone, then by depositing a conductiveelement on this insulating layer so as to connect one outside end of theantenna to one connection pad.

Another method of producing the insulating bridge consists in formingthe antenna on each side of the support sheet, the connection pads beingproduced on the same side of the support sheet.

In addition, in the solution approved by the prior art, since the bodyof the card consists of a stack of several foils, the perforationsformed in each foil must be superimposed. However, during the laminatingstage the geometry of the perforations is not controlled and canfluctuate. Moreover, during this laminating stage the pressure becomeszero perpendicularly to the perforations whereas it is high over thebody of the card. This difference in pressure causes the creation of afault in the surface of the cards.

To avoid this problem of the deformation of the card, the inventionproposes, in addition, to assemble together all the plastic foils whichform the body of the card and then to machine the body of the card toform the cavity for the electronic module and the connection recessesprovided to expose the connection pads of the antenna.

This machining is preferably done in a single stage, this being madepossible thanks to the precise control of the position of the antenna inrelation to the position of the cavity.

The fact that the cavity and the connecting recesses are machinedsimultaneously greatly simplifies and accelerates the manufacturingmethod.

In addition, the invention proposes a second solution to the problem ofthe risk of damaging or even destroying the antenna. It proposes,indeed, a method for manufacturing a smart card, said smart cardcomprising an antenna at the ends of which are provided pads connectingit to the electronic module, characterised in that the method comprisesat least one stage consisting in machining a cavity and connectingrecesses in an upper face of the body of the card, in such a way thatthe machining plane of the bottom of the cavity is situated above theplane of the antenna and the connection recesses are situated above theconnection pads of the antenna and allow them to be exposed.

In addition, the connecting elements between the module and the antenna,which will be called the interconnection in what follows, can be damagedduring testing of the cards by bending and twisting. To minimise thestresses on the interconnection during these tests the inventionproposes that the antenna be located in an area of the card where thestresses are lowest. Thus, the foil supporting the antenna is located onor near the elastic neutral axis of the card. The neutral axis of a cardis defined as being the layer situated at the centre of the thickness ofthe card.

In addition, after the machining of the cavity the antenna is generallyconnected to the electronic module by filling the connecting recesseswith a conductive adhesive. When the module is installed in the card theheating time is too short to ensure correct polymerisation of theadhesive. In these conditions cards must spend a long period in an oven.In addition, given that the maximum temperature which the body of thecard can withstand is generally below 100° C., it is difficult to ensurea good interconnection without deforming the body of the card. As aresult, the manufacture of the card in these conditions is long anddifficult, and cannot be adapted to mass-production.

The invention provides different solutions to this problem ofinterconnection. In particular, it proposes the use of a solder with lowmelting point, that is, a melting point well below 180° C., to producethe connection between the connection pads of the antenna and theelectronic module. To this end, the solder comprises an alloy with abasis of indium and tin, or with a basis of bismuth, tin and lead, orwith a basis of bismuth, indium and tin.

According to other characteristics, the connection between theconnection pads of the antenna and the electronic module is formed bymeans of a conductive grease, or by means of a silicon gasket chargedwith metallic particles.

BRIEF DESCRIPTION OF THE FIGURES

Other features and advantages of the invention will emerge from areading of the description given by way of a non-limiting example, withreference to the attached drawings, in which

FIG. 1 shows a schematic perspective view of an antenna of a smart cardformed on a support sheet,

FIG. 2 shows a schematic sectional view of an insulating bridge of theantenna of FIG. 1,

FIG. 3 shows a schematic perspective view of another method of producingan antenna of a smart card,

FIG. 4 shows a schematic perspective view of another method of producingan antenna of a smart card,

FIGS. 5A to 5C show sectional views of a card during different stages ofa manufacturing process according to the invention,

FIG. 6 shows a schematic sectional view of a card produced according toanother manufacturing method according to the invention

FIG. 7A shows a top view of the flush contacts of a single-sided module,

FIG. 7B shows a perspective view illustrating the position of theconnection recesses in relation to a cavity formed in the body of acard,

FIGS. 7C and 7D show two views of contacts on the interior face ofdouble-sided modules,

FIG. 7E shows a perspective view illustrating the position of theconnection recesses in the cavity.

DETAILED DESCRIPTION

In general, mixed smart cards will be produced by the bonding (hot orcold lamination) of foils of plastic material in which the antennaconductor has been inserted or interposed; then by forming a cavity inthe assembled foils, between the connection pads provided at the ends ofthe antenna conductor, in order to create a space intended toaccommodate the electronic module with integrated circuit; and byinstalling this module so that two conductive pads of the module comeinto electrical contact with the connection pads of the antennaconductor, either directly or, more frequently, through the intermediaryof a conductive linking element.

FIG. 1 shows a first method of producing an antenna 11 comprising atleast two turns and intended to be enclosed in the body of a contactlesssmart card. Two connection pads 12 are provided at the ends of theantenna filament 11. An important stage in a manufacturing method ofsuch a contactless smart card consists in producing the antenna 11, on asupport sheet 10, in such a way as to define precisely its position inthe body of the card in relation to the position of a cavity to bemachined and intended to accommodate the electronic module.

According to a first manner of production, the turns of this antenna 11are located outside the connection pads 12, and an insulating bridge 13is formed so as to connect each end of the antenna to a connection pad12 respectively, without creating a short-circuit. This manner ofproduction allows a free space to be located between the connection pads12 of the antenna 11, since no turn passes through it. The free spacehaving been formed, the tracks of the antenna do not risk being damagedduring a later stage when the cavity for the micromodule is machined,and the positioning tolerances are greatly increased.

FIG. 2 shows a sectional view along A-A of FIG. 1 and shows theinsulating bridge 13 of the antenna 11. This insulating bridge 13 isproduced by covering the turns of antenna 11 with an insulating layer 14in a zone Z, then by depositing a conductive element 15 on thisinsulating layer 14, the conductive element 15 allowing the end of oneturn, and in particular the end of the last turn situated the furthesttowards the outside of the support sheet 10, to be connected to one ofthe connection pads 12 of the antenna.

According to another method of production, illustrated in FIGS. 3 and 4,the antenna 11 is formed on each side of the support sheet 10. In thiscase, connecting paths (metallic holes) 16, 17 are formed in the supportsheet. The connection pads 12 of the antenna are formed on one face. Theinsulating bridge 13 is therefore produced by means of metallic holes toprovide the connection between the antenna filaments located on eachside of the support sheet 12 [sic], as shown schematically by brokenlines in FIGS. 3 and 4.

The insulating bridge 13 thus allows the turns of the antenna to crosswithout directly overlapping and therefore without causingshort-circuits.

After having produced this antenna on the support sheet 10, of plasticmaterial, this support sheet 10 is assembled with other plastic sheetsor foils 20, 30, 40, 50 and the sheets are bonded together by hot orcold lamination. This assembly stage is illustrated in FIG. 5A.

Foils 20 and 40 represent the upper and lower foils, which may beprinted, of the body of the card. Foils 30 and 50 are upper and lowerprotective foils respectively, and are intended to protect the printedfoils 20 and 40.

In one variant of the realisation, it is possible to add a sixth plasticfoil and to position it just above the support sheet 10 in order toenclose antenna 11.

A later stage, illustrated in FIG. 5B, consists in machining a cavity 61and connection recesses 62 in an upper face of the body of the cardformed by the assembly of foils 10, 20, 30, 40 and 50. This machiningmay be done, for example, in a single stage.

The machining plane of cavity 61 is situated lower than the connectionpads 12 of antenna 11. The connection recesses 62 are situated above theconnection pads 12 of the antenna and enable these pads to be exposed.

The cavity and the connection recesses are machined by means of amilling cutter the feed depth of which is controlled.

The last stage of the procedure, shown in FIG. 5C, then consists infixing an electronic module M in the cavity 61. The module M compriseson its lower side, facing towards the inside of the cavity, conductivepads 72 in electrical contact with connection pads 12 of the antenna bymeans of a conductive linking element 66 located in the connectionrecesses 62. The way in which the connection between the module and theantenna is established is explained in more detail in what follows.

A procedure for manufacturing a mixed smart card according to adifferent method of production and illustrated in FIG. 6 can beadditionally envisaged to position the antenna precisely in relation tothe cavity of the module.

According to this other method of realisation, antenna 11 is produced inthe conventional way on a support sheet; that is, the turns of theantenna pass between the connection pads 12. The sheet supporting theantenna is then assembled with the other plastic foils; then the cavity61 and the connection recesses 62 are machined in the upper surface ofthe body of the card formed by the assembly of foils. This stage iscarried out in such a way that the machining plane of the bottom of thecavity 61 is situated above the plane of the tracks of the antenna 11and that the connection recesses 62 are situated above the connectionpads 12 of the antenna, enabling them to be exposed. The electronicmodule M is then fixed in the cavity and its conductive pads 72 areelectrically connected to the connection pads 12 of the antenna throughthe connection recesses 62.

In all cases, the antenna 11 can be produced by incrustation on aplastic support sheet. The incrustation is carried out in a known mannerby an ultrasound process.

Moreover, to minimise the stresses on the interconnection, especiallyduring testing of the cards by bending or twisting, the inventionproposes that the antenna be located on the elastic neutral axis of thecard. Thus, it is envisaged that the sheet 10 supporting the antenna belocated so as to form the neutral axis of the card. The neutral axis ofa card is defined as being located at the centre of the thickness of thecard.

In addition, in one variant of the procedure according to the inventionit is possible to carry out the machining in such a way that theconnection recesses pass through the connection pads 12 of the antenna.In this case, the electronic module is connected laterally, that is,through the cut edges of the connection pads, by applying a conductiveconnecting element to the connection recesses and to the lateral edgesof the connection pads.

In general, the contact surface of the connection pads of the antenna issmall, since it is of the same order of magnitude as the width of theconductive filament used to form the antenna (that is, some ten[s of]μm). As a result, the interconnection with the electronic module isdifficult to carry out since it requires a high degree of precision. Itis therefore preferable to produce the connection pads 12 such that theypresent a zigzag pattern in order to increase their contact surface.This zigzag pattern is produced by twists in the antenna filament (seeFIGS. 1, 3, 4).

The module M can be a single-sided printed circuit module or adouble-sided printed circuit module, and in the latter case it can havetwo possible configurations, to which this description will returnlater.

A module M is shown in FIGS. 5 and 6 above the cavity 61. In theseexamples it is a double-sided printed circuit module comprising upperconductors 70 on the side which will face towards the outside of thecavity and lower conductors 72 on the side which will face towards theinside of the cavity. The conductors are formed on an insulating foil 80and conductive paths which can link the upper conductors 70 and thelower conductors 72 [are provided]. A microchip embedded in a protectiveresin 74 is mounted on the lower face and connected to conductors 72(and through them to conductors 70).

The module fits into the cavity 61 which has been machined to itsdimensions. Two conductive pads of the lower face of the module, locatedjust above the connection pads 12 of the antenna, are connectedelectrically to these two connection pads by a conductive linkingelement 66.

In one particularly interesting variant of the realisation, the moduleconsists of a double-sided printed circuit carrying theintegrated-circuit microchip, but this double-sided circuit is formedwithout a conductive path between the conductors on the two faces,making it less costly. In this case, the double-sided circuit comprisesan insulating foil 80 carrying on one face a first set of conductivepads 70 intended to serve as access contacts to the smart card and onthe other face a second set of conductive pads 72 intended to beconnected to the antenna. Connecting filaments are soldered between themicrochip and the first conductive pads through open zones of theinsulating foil and other linking filaments are soldered between themicrochip and the second set of conductive pads without passing throughthe insulating foil.

The definition of a single-sided module for a mixed card consists infinding the position of the contacts for the antenna, which presents thefollowing difficulties:

-   -   the contact zones defined by ISO and AFNOR standards cannot        receive the contacts of the antenna since this can cause        short-circuiting of the reader,    -   on the assembly side, the resin protecting the microchip and the        bonding resin eliminates the central zone of the module,    -   the performance of the card with regard to resistance to bending        necessitates the presence of a preferential deformation line        without producing zones of embrittlement of the metal on the        contact side.

FIG. 7A shows schematically a top view of the flush contacts of a smartcard with a single-sided module which responds to these problems. Themodule comprises contact pads 1, 2, 3, 4, 5 and 1′, 2′, 3′ 4′ and 5′,the positions of which are standardised by ISO and AFNOR standards.These contact pads are connected to the microchip to enable the moduleto operate. The position of the contact zones to be used to connect themodule to the antenna can only be situated in the upper zones 6 and 7and the lower zones 8 and 9 on either side of an axis 65 of the module,that is, outside the contact zones defined by the ISO standard.

In these conditions, therefore, the positions of the connection pads ofthe antenna and of the connection recesses in the body of the card arelimited by the standardised position of the contact zones of theelectronic module and by the position of this module in the body of thecard, which is itself defined by the ISO standards.

FIG. 7B illustrates the case in which the connection recesses 62, andtherefore the corresponding connection pads, are situated side-by-sideand on each side of the mid-perpendicular 65 of the cavity 61. This casecorresponds to the case in which the contact zones 6 and 7 of the modulein FIG. 7A are electrically connected to the connection pads of theantenna.

Furthermore, the use of a double-sided module must also be able toovercome the disadvantages mentioned with regard to the single-sidedmodule.

The contacts illustrated in FIGS. 7C and 7D provide a solution to theseproblems. In particular, the presence of two tracks 100, 101 on eitherside of the circuit allows different configurations of microchips to beconnected to the same module.

These two methods of producing the contacts for the double-sided modulecomprise at least one track with its edge parallel to the microchip,connected to contact zones 110 and 120. These zones 110 and 120represent the possible contact zones with the antenna.

FIG. 7E illustrates the case in which the connection recesses 62, andtherefore the connection pads of the antenna, are diametrically oppositeeach other and situated on a mid-perpendicular 65 of the cavity. Thiscase corresponds to that in which the contact zones 110 and 120 of themodule in FIG. 7C are electrically connected to the connection pads ofthe antenna.

FIGS. 7B and 7E illustrate connection recesses formed continuously withthe cavity, giving them the special shape shown in the diagrams. Ofcourse, these recesses could be formed non-continuously with the cavityand appear as holes of any shape provided that their positioning is asdefined previously.

The interconnection between the electronic module and the antenna may bemade with the aid of a conductive linking element of the type of solder.However, in general the remelt temperature of these products is veryhigh, in the region of 180° C. These temperatures are incompatible withthe plastic materials used to form the body of the card, which cannotwithstand temperatures much above 100° C.

The invention proposes that a solder with low melting point be used toensure good compatibility with the card body. For this, it is preferableto use a solder comprising an alloy with a basis of indium and tin, orwith a basis of bismuth, tin and lead, or a basis of bismuth, tin andindium.

In the case of an alloy of indium and tin, the solder comprises not morethan 52% by weight of indium and 48% by weight of tin. With thiscomposition the melting point of the solder is 118° C.

In the case of an alloy of bismuth, tin and lead, the solder comprisesnot more than 46% by weight of bismuth and 34% by weight of tin and 20%by weight of lead. With this composition the melting point of the solderis 100° C.

In the case of an alloy of bismuth, indium and tin, the solder comprisesnot more than 57% by weight of bismuth, 26% by weight of indium and 17%by weight of tin. With this composition the melting point of the solderis 79° C.

Another method of producing the interconnection consists in depositingconductive grease charged with metallic particles in the connectionrecesses. Contact is then made by friction and ensures electricalconduction between the antenna and the module, and does so regardless ofthe mechanical stresses applied to the card.

A third method of producing the interconnection consists in using asilicon gasket charged with metallic particles. This solution has theadvantage of providing a very supple connecting joint. In this case, thedimensions of the silicone gasket are greater than the depth of theconnection recesses so that the silicon is compressed and the metallicparticles are brought into contact.

Regardless of which solution is adopted, the reliability of theinterconnection between the antenna and the module can be increased byusing balls of gold deposited on the conductive pads 72 of the module.These balls of gold do not provide the connection but increase thebonding surface and modify the distribution of stresses in theconductive joint when the card is subjected to mechanical loads. Theseballs are deposited by thermo-compression. Moreover, they can be stackedin order to increase the height of the contact surface.

1. A smart card, comprising: an antenna winding with at least two turnsand a pair of ends that are respectively associated with two connectionpoints, said antenna being incrusted on a support sheet and including alink that crosses said turns to connect the end of one of said turns toone of said connection points, with said link being insulated from saidturns to avoid a short circuit.
 2. A smart card according to claim 1,further including an integrated circuit chip connected to saidconnection pads.
 3. A smart card according to claim 1, wherein said linkconnects the end of the outside turn to a connection point locatedwithin the interior of said turns.
 4. A smart card, comprising: anantenna winding with at least two turns, a pair of connection pads bothdisposed on a common side of said antenna winding, an insulatingmaterial covering a zone across said antenna winding, and a conductiveelement on said insulating material that connects an end of said windingon a side opposite said common side to one of said connection pads.
 5. Asmart card according to claim 4, further including an integrated circuitchip connected to said connection pads.